Determining the location of standard, wireless radio frequency (RF), communications transmitter/receivers ("transceivers") based on their communications offers the potential for emergency response services (fire, rescue and police) to more rapidly respond to calls for help. Public safety and private security can all be aided by making available information concerning position and geographic location. Technologies, such as those disclosed herein, do not require modifying standard communications devices in any way to facilitate the real-time determination of their locations.
The communications transceivers most popularly used by the general public are the mobile units (i.e., "telephones") of cellularized communications systems. Examples included the "cellular telephone" and "personal communications service" (PCS) systems. Cellular communications systems typically use control-data messages to "manage" the transmitted power level of a mobile unit to limit its transmitted level to only that needed for successful communications reception within the controlling local "cell." This power management can limit the reception of the communications transmissions at multiple receiver sites and thus make more difficult the task of determining the transmitter's location. Furthermore, when in use for communication, the wireless telephones are dedicated to voice or "traffic" transmission channels rather than control or "access" channels. Thus, facilities are needed to locate the transmitters on any type of channel.
The present invention addresses these issues by providing robust and efficient means to extract parametric measurements from either or both of voice and control communications signals. These measurements can then be used to support the localization processing that is needed to locate wireless communications transceivers. Location data can be used to rapidly rout wireless calls to someone, or some agency, who is in a position to respond to the call. Thus, the location information can support swift response to wireless emergency "9-1-1" calls. Other requests, such as for non-emergency assistance or position-related, "yellow pages" information, also can be addressed. Motion data can be generated from the location data; such data can be used for monitoring transportation congestion as well as for vehicle fleet management.
The present invention can advance the performance and cost efficiency of a variety of system approaches to the localization of standard, wireless, mobile communications transmitters. Various techniques have been disclosed that are intended to provide the utility and meet the need of such systems. As the pioneer of such technologies, U.S. Pat. No. 4,728,959 discloses, among other novel features, a system with a means for measuring a direction angle of the mobile radio transmitter station from at least two land stations by phase difference measurement, including means for performing a phase sensitive weighted integration of a complex conjugate product of an equivalent signal in each antenna element. This allows for, among other things, measuring the angle-of-arrival (AOA) of a signal from a mobile transceiver based on the covariances of the elemental signals received with phased arrays at distributed sensor sites, and to thereby obtain and provide the location of a standard mobile communications transmitter.
The present invention advances the state of the art in AOA systems by using matched-replica correlations to enhance their robustness and to extend the applicability of such fundamental concepts into the domain of severe co-channel interference. Co-channel interference is a particular problem and inherent with a type of digital communication system known as code-division-multiple-access (CDMA) communications. Systems exist which purport to provide locations for standard mobile transmitters by extracting measurements from "beamformed" signals using time-difference-of-arrival (TDOA) correlations of the direct, sampled, representations of the signals themselves, given sufficient signal bandwidth (which is often not available from most commercial "analog" transceivers). The transmitting may (adaptively) mitigate some multipath signal propagation effects. However, to actually implement such correlation processing, the sampled signal representations must be collected at a common correlation site. Such signal collection requires supporting "back-haul" communication of the significant volumes of data that make up the representations of the sampled signals.
It is an objective of the present invention to extend the utility of AOA and TDOA- based localization concepts so as to be applicable to signals that are not necessarily the product, and do not entail the expense, of beamforming. It is also an objective of the present invention to advance the effectiveness of the correlation processing through the use of matched-replica processing, which provides a distortion-free representation of the signal to the correlator for enhanced correlation detectability. It is also an objective of the present invention to improve the efficiency of the integrated system processing by eliminating the need for any inter-site back-haul communication of representative signal data when the signal replica can be locally derived from the received signal and/or from a known stored replica. It is also an objective of the present invention to significantly reduce the quantity of representative signal data that is transferred between sites through the extraction and use of the demodulated forms of the information content that is in the RF transmissions for all forms of modulation.
U.S. Pat. No. 5,327,144 discloses a system with purports to measure signal time-of-arrival (TOA), and associated time-difference-of-arrival (TDOA) approach using what is described as correlation processing. However, the technique described requires extensive inter-site, back-haul communications of sampled signal representations or the less extensive demodulated replicas. Such communications are apparently used to provide locations for standard mobile transmitters in cellularized communications "systems that employ analog control channels," through the exploitation of the short-duration, "bursty" (control) signals. In the United States, the "analog" signal formats, for the "air interface" between the mobile transceiver and the communications system infrastructure use the Advanced Mobile Phone System (AMPS) specification. The AMPS control messages occur in bursts that are approximately one tenth of a second in duration.
The present invention enhances the utility of the correlative derivation of any measurements by eliminating requirements for bursty, analog, control signals and for the back-haul communications of signal representations. The present invention further extends the applicability of the matched-replica processing to enable the processing of signals of "continuous" or opportunistic (rather than merely induced or transponded) transmissions as well as of transmissions of digital formats, such as of voice signals in CDMA systems. Furthermore, the present invention also extends matched-replica correlative processing to provide robust and efficient measures of AOAs, as well as TOAs or TDOAs, for all of the communications signal formats.
The present invention provides a system that effectively determines location-sensitive parameters for, and locates and/or tracks, a standard, mobile-communications, radio transmitter in a cellularized communications system. The system uses replica correlation processing, and associated representative signal-data reduction and reconstruction techniques, to detect signals of interest and obtain robust measures of location-related, received-signal parameters, such as time differences of signal arrival (TDOAs) and directional angles of arrival (AOAs), for the estimation of the locations of cellularized-communications signal sources. The new use in the present invention of signal-correlation processing to support the localization of the communications transmitters enables accurate and efficient extraction of parameters for a particular signal even in a frequency band that contains multiple received transmissions, such as occurs with code-division-multiple-access (CDMA) communications.
The use in the present invention of correlation processing further enables extended processing integration times to facilitate the effective detection of desired communications-signal effects and enhanced measurement of their location-related parameters, even for the communications signals modulated to convey voice conversations or those weakened through propagation effects. When derivable from the received transmissions themselves, such as with sufficiently strong modulated signals representing digital information, or when otherwise available, such as with communications-control or other known-data contents in the received transmissions, the use in the present invention of reconstructed signal replicas in the correlation processing enables elimination of the inter-site communications of the signal representations that support the correlation analyses. The use in the present invention of reduced-data representations of the modulated signals for voiced conversation, or for the variable components of data communications, significantly reduces the inter-site communications that support the correlation analyses. Thus, the present invention significantly enhances the robustness, applicability, and efficiency, and reduces the cost of implementation, of correlation techniques for the detection and measurement of signal parameters to support the localization and tracking of the wireless communications transmitters used in cellularized or geographically subdivided communications systems.
All of the foregoing objectives, features and advantages of the present invention, and more, are explained below with the aid of the following illustrative figures and exemplary embodiments.